[PATCH] powerpc/kernel: improve FP and vector registers restoration

[Breno Leitao]

Currently tsk->thread->load_vec and load_fp are not initialized during a
task creation, which set garbage to these variables (non-zero value).

These variables will be checked later at restore_math() to validate if the
FP and vectors are being utilized. Since these values might be non-zero,
the restore_math() will continue to save the FP and vectors even if they
were never utilized before the userspace application. load_fp and load_vec
counters will then overflow and the FP and Altivec will be finally
disabled, but before that condition is reached (counter overflow) several
context switches restored FP and vector registers without need, causing a
performance degradation.

Signed-off-by: Breno Leitao <breno.leitao at gmail.com>
Signed-off-by: Gustavo Romero <gusbromero at gmail.com>
---
 arch/powerpc/kernel/process.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index baae104b16c7..a9435397eab8 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -1666,6 +1666,7 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
 #ifdef CONFIG_VSX
 	current->thread.used_vsr = 0;
 #endif
+	current->thread.load_fp = 0;
 	memset(&current->thread.fp_state, 0, sizeof(current->thread.fp_state));
 	current->thread.fp_save_area = NULL;
 #ifdef CONFIG_ALTIVEC
@@ -1674,6 +1675,7 @@ void start_thread(struct pt_regs *regs, unsigned long start, unsigned long sp)
 	current->thread.vr_save_area = NULL;
 	current->thread.vrsave = 0;
 	current->thread.used_vr = 0;
+	current->thread.load_vec = 0;
 #endif /* CONFIG_ALTIVEC */
 #ifdef CONFIG_SPE
 	memset(current->thread.evr, 0, sizeof(current->thread.evr));
-- 
2.11.0